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  <div class="SECT1">
    <h1 class="SECT1"><a name="MISC" id="MISC">4. Miscellaneous</a></h1>

    <div class="SECT2">
      <h3 class="SECT2"><a name="AEN738" id="AEN738">4.1. How much does
      Privoxy slow my browsing down? This has to add extra time to
      browsing.</a></h3>

      <p>How much of an impact depends on many things, including the CPU of
      the host system, how aggressive the configuration is, which specific
      actions are being triggered, the size of the page, the bandwidth of the
      connection, etc.</p>

      <p>Overall, it should not slow you down any in real terms, and may
      actually help speed things up since ads, banners and other junk are not
      typically being retrieved and displayed. The actual processing time
      required by <span class="APPLICATION">Privoxy</span> itself for each
      page, is relatively small in the overall scheme of things, and happens
      very quickly. This is typically more than offset by time saved not
      downloading and rendering ad images and other junk content (if ad
      blocking is being used).</p>

      <p><span class="QUOTE">"Filtering"</span> content via the <tt class=
      "LITERAL"><a href="../user-manual/actions-file.html#FILTER" target=
      "_top">filter</a></tt> or <tt class="LITERAL"><a href=
      "../user-manual/actions-file.html#DEANIMATE-GIFS" target=
      "_top">deanimate-gifs</a></tt> actions may cause a perceived slowdown,
      since the entire document needs to be buffered before displaying. And
      on very large documents, filtering may have some measurable impact. How
      much depends on the page size, the actual definition of the filter(s),
      etc. See below. Most other actions have little to no impact on
      speed.</p>

      <p>Also, when filtering is enabled but zlib support isn't available,
      compression is often disabled (see <a href=
      "../user-manual/actions-file.html#PREVENT-COMPRESSION" target=
      "_top">prevent-compression</a>). This can have an impact on speed as
      well, although it's probably smaller than you might think. Again, the
      page size, etc. will determine how much of an impact.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="LOADINGTIMES" id="LOADINGTIMES">4.2. I
      notice considerable delays in page requests. What's wrong?</a></h3>

      <p>If you use any <tt class="LITERAL"><a href=
      "../user-manual/actions-file.html#FILTER" target="_top">filter</a></tt>
      action, such as filtering banners by size, web-bugs etc, or the
      <tt class="LITERAL"><a href=
      "../user-manual/actions-file.html#DEANIMATE-GIFS" target=
      "_top">deanimate-gifs</a></tt> action, the entire document must be
      loaded into memory in order for the filtering mechanism to work, and
      nothing is sent to the browser during this time.</p>

      <p>The loading time typically does not really change much in real
      numbers, but the feeling is different, because most browsers are able
      to start rendering incomplete content, giving the user a feeling of "it
      works". This effect is more noticeable on slower dialup connections.
      Extremely large documents may have some impact on the time to load the
      page where there is filtering being done. But overall, the difference
      should be very minimal. If there is a big impact, then probably some
      other situation is contributing (like anti-virus software).</p>

      <p>Filtering is automatically disabled for inappropriate MIME types.
      But note that if the web server mis-reports the MIME type, then content
      that should not be filtered, could be. <span class=
      "APPLICATION">Privoxy</span> only knows how to differentiate filterable
      content because of the MIME type as reported by the server, or because
      of some configuration setting that enables/disables filtering.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="CONFIGURL" id="CONFIGURL">4.3. What are
      "http://config.privoxy.org/" and "http://p.p/"?</a></h3>

      <p><a href="http://config.privoxy.org/" target=
      "_top">http://config.privoxy.org/</a> is the address of <span class=
      "APPLICATION">Privoxy</span>'s built-in user interface, and <a href=
      "http://p.p/" target="_top">http://p.p/</a> is a shortcut for it.</p>

      <p>Since <span class="APPLICATION">Privoxy</span> sits between your web
      browser and the Internet, it can simply intercept requests for these
      addresses and answer them with its built-in <span class="QUOTE">"web
      server"</span>.</p>

      <p>This also makes for a good test for your browser configuration: If
      entering the URL <a href="http://config.privoxy.org/" target=
      "_top">http://config.privoxy.org/</a> takes you to a page saying
      <span class="QUOTE">"This is Privoxy ..."</span>, everything is OK. If
      you get a page saying <span class="QUOTE">"Privoxy is not
      working"</span> instead, then your browser didn't use <span class=
      "APPLICATION">Privoxy</span> for the request, hence it could not be
      intercepted, and you have accessed the <span class=
      "emphasis EMPHASIS c2">real</span> web site at config.privoxy.org.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="NEWADS" id="NEWADS">4.4. How can I submit
      new ads, or report problems?</a></h3>

      <p>Please see the <a href="contact.html">Contact section</a> for
      various ways to interact with the developers.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="NEWADS2" id="NEWADS2">4.5. If I do submit
      missed ads, will they be included in future updates?</a></h3>

      <p>Whether such submissions are eventually included in the <tt class=
      "FILENAME">default.action</tt> configuration file depends on how
      significant the issue is. We of course want to address any potential
      problem with major, high-profile sites such as <i class=
      "CITETITLE">Google</i>, <i class="CITETITLE">Yahoo</i>, etc. Any site
      with global or regional reach, has a good chance of being a candidate.
      But at the other end of the spectrum are any number of smaller,
      low-profile sites such as for local clubs or schools. Since their reach
      and impact are much less, they are best handled by inclusion in the
      user's <tt class="FILENAME">user.action</tt>, and thus would be
      unlikely to be included.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="NOONECARES" id="NOONECARES">4.6. Why doesn't
      anyone answer my support request?</a></h3>

      <p>Rest assured that it has been read and considered. Why it is not
      answered, could be for various reasons, including no one has a good
      answer for it, no one has had time to yet investigate it thoroughly, it
      has been reported numerous times already, or because not enough
      information was provided to help us help you. Your efforts are not
      wasted, and we do appreciate them.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="IP" id="IP">4.7. How can I hide my IP
      address?</a></h3>

      <p>If you run both the browser and <span class=
      "APPLICATION">Privoxy</span> locally, you cannot hide your IP address
      with <span class="APPLICATION">Privoxy</span> or ultimately any other
      software alone. The server needs to know your IP address so that it
      knows where to send the responses back.</p>

      <p>There are many publicly usable "anonymous" proxies out there, which
      provide a further level of indirection between you and the web
      server.</p>

      <p>However, these proxies are called "anonymous" because you don't need
      to authenticate, not because they would offer any real anonymity. Most
      of them will log your IP address and make it available to the
      authorities in case you violate the law of the country they run in. In
      fact you can't even rule out that some of them only exist to *collect*
      information on (those suspicious) people with a more than average
      preference for privacy.</p>

      <p>If you want to hide your IP address from most adversaries, you
      should consider chaining <span class="APPLICATION">Privoxy</span> with
      <a href="https://www.torproject.org/" target="_top">Tor</a>. The
      configuration details can be found in <a href="#TOR" target="_top">How
      do I use <span class="APPLICATION">Privoxy</span> together with
      <span class="APPLICATION">Tor</span> section</a> just below.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="AEN803" id="AEN803">4.8. Can Privoxy
      guarantee I am anonymous?</a></h3>

      <p>No. Your chances of remaining anonymous are improved, but unless you
      <a href="#TOR" target="_top">chain <span class=
      "APPLICATION">Privoxy</span> with <span class=
      "APPLICATION">Tor</span></a> or a similar proxy and know what you're
      doing when it comes to configuring the rest of your system, you should
      assume that everything you do on the Web can be traced back to you.</p>

      <p><span class="APPLICATION">Privoxy</span> can remove various
      information about you, and allows <span class=
      "emphasis EMPHASIS c2">you</span> more freedom to decide which sites
      you can trust, and what details you want to reveal. But it neither
      hides your IP address, nor can it guarantee that the rest of the system
      behaves correctly. There are several possibilities how a web sites can
      find out who you are, even if you are using a strict <span class=
      "APPLICATION">Privoxy</span> configuration and chained it with
      <span class="APPLICATION">Tor</span>.</p>

      <p>Most of <span class="APPLICATION">Privoxy's</span> privacy-enhancing
      features can be easily subverted by an insecure browser configuration,
      therefore you should use a browser that can be configured to only
      execute code from trusted sites, and be careful which sites you trust.
      For example there is no point in having <span class=
      "APPLICATION">Privoxy</span> modify the User-Agent header, if websites
      can get all the information they want through JavaScript, ActiveX,
      Flash, Java etc.</p>

      <p>A few browsers disclose the user's email address in certain
      situations, such as when transferring a file by FTP. <span class=
      "APPLICATION">Privoxy</span> does not filter FTP. If you need this
      feature, or are concerned about the mail handler of your browser
      disclosing your email address, you might consider products such as
      <span class="APPLICATION">NSClean</span>.</p>

      <p>Browsers available only as binaries could use non-standard headers
      to give out any information they can have access to: see the
      manufacturer's license agreement. It's impossible to anticipate and
      prevent every breach of privacy that might occur. The professionally
      paranoid prefer browsers available as source code, because anticipating
      their behavior is easier. Trust the source, Luke!</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="AEN821" id="AEN821">4.9. A test site says I
      am not using a Proxy.</a></h3>

      <p>Good! Actually, they are probably testing for some other kinds of
      proxies. Hiding yourself completely would require additional steps.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="TOR" id="TOR">4.10. How do I use Privoxy
      together with Tor?</a></h3>

      <p>Before you configure <span class="APPLICATION">Privoxy</span> to use
      <a href="https://www.torproject.org/" target="_top">Tor</a>, please
      follow the <i class="CITETITLE">User Manual</i> chapters <a href=
      "../user-manual/installation.html" target="_top">2. Installation</a>
      and <a href="../user-manual/startup.html" target="_top">5. Startup</a>
      to make sure <span class="APPLICATION">Privoxy</span> itself is setup
      correctly.</p>

      <p>If it is, refer to <a href=
      "https://www.torproject.org/documentation.html" target="_top">Tor's
      extensive documentation</a> to learn how to install <span class=
      "APPLICATION">Tor</span>, and make sure <span class=
      "APPLICATION">Tor</span>'s logfile says that <span class="QUOTE">"Tor
      has successfully opened a circuit"</span> and it <span class=
      "QUOTE">"looks like client functionality is working"</span>.</p>

      <p>If either <span class="APPLICATION">Tor</span> or <span class=
      "APPLICATION">Privoxy</span> isn't working, their combination most
      likely will neither. Testing them on their own will also help you to
      direct problem reports to the right audience. If <span class=
      "APPLICATION">Privoxy</span> isn't working, don't bother the
      <span class="APPLICATION">Tor</span> developers. If <span class=
      "APPLICATION">Tor</span> isn't working, don't send bug reports to the
      <span class="APPLICATION">Privoxy</span> Team.</p>

      <p>If you verified that <span class="APPLICATION">Privoxy</span> and
      <span class="APPLICATION">Tor</span> are working, it is time to connect
      them. As far as <span class="APPLICATION">Privoxy</span> is concerned,
      <span class="APPLICATION">Tor</span> is just another proxy that can be
      reached by socks4, socks4a and socks5. Most likely you are interested
      in <span class="APPLICATION">Tor</span> to increase your anonymity
      level, therefore you should use socks5, to make sure DNS requests are
      done through <span class="APPLICATION">Tor</span> and thus invisible to
      your local network. Using socks4a would work too, but with socks5 you
      get more precise error messages.</p>

      <p>Since <span class="APPLICATION">Privoxy</span> 3.0.5, its <a href=
      "../user-manual/config.html" target="_top">main configuration file</a>
      is already prepared for <span class="APPLICATION">Tor</span>, if you
      are using a default <span class="APPLICATION">Tor</span> configuration
      and run it on the same system as <span class=
      "APPLICATION">Privoxy</span>, you just have to edit the <a href=
      "../user-manual/config.html#FORWARDING" target="_top">forwarding
      section</a> and uncomment the line:</p>

      <table class="c3" border="0" width="100%">
        <tr>
          <td>
            <pre class="SCREEN">
#        forward-socks5             /     127.0.0.1:9050 .

</pre>
          </td>
        </tr>
      </table>

      <p>This is enough to reach the Internet, but additionally you might
      want to uncomment the following forward rules, to make sure your local
      network is still reachable through Privoxy:</p>

      <table class="c3" border="0" width="100%">
        <tr>
          <td>
            <pre class="SCREEN">
#        forward         192.168.*.*/     .
#        forward            10.*.*.*/     .
#        forward           127.*.*.*/     .

</pre>
          </td>
        </tr>
      </table>

      <p>Unencrypted connections to systems in these address ranges will be
      as (un)secure as the local network is, but the alternative is that your
      browser can't reach the network at all. Then again, that may actually
      be desired and if you don't know for sure that your browser has to be
      able to reach the local network, there's no reason to allow it.</p>

      <p>If you want your browser to be able to reach servers in your local
      network by using their names, you will need additional exceptions that
      look like this:</p>

      <table class="c3" border="0" width="100%">
        <tr>
          <td>
            <pre class="SCREEN">
#        forward           localhost/     .

</pre>
          </td>
        </tr>
      </table>

      <p>Save the modified configuration file and open <a href=
      "http://config.privoxy.org/show-status" target=
      "_top">http://config.privoxy.org/show-status/</a> in your browser,
      confirm that <span class="APPLICATION">Privoxy</span> has reloaded its
      configuration and that there are no other forward lines, unless you
      know that you need them. If everything looks good, refer to <a href=
      "https://wiki.torproject.org/noreply/TheOnionRouter/TorFAQ#IsMyConnectionPrivate"
      target="_top">Tor Faq 4.2</a> to learn how to verify that you are
      really using <span class="APPLICATION">Tor</span>.</p>

      <p>Afterward, please take the time to at least skim through the rest of
      <span class="APPLICATION">Tor's</span> documentation. Make sure you
      understand what <span class="APPLICATION">Tor</span> does, why it is no
      replacement for application level security, and why you probably don't
      want to use it for unencrypted logins.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="AEN877" id="AEN877">4.11. Might some things
      break because header information or content is being altered?</a></h3>

      <p>Definitely. It is common for sites to use browser type, browser
      version, HTTP header content, and various other techniques in order to
      dynamically decide what to display and how to display it. What you see,
      and what I see, might be very different. There are many, many ways that
      this can be handled, so having hard and fast rules, is tricky.</p>

      <p>The <span class="QUOTE">"User-Agent"</span> is sometimes used in
      this way to identify the browser, and adjust content accordingly.</p>

      <p>Also, different browsers use different encodings of non-English
      characters, certain web servers convert pages on-the-fly according to
      the User Agent header. Giving a <span class="QUOTE">"User Agent"</span>
      with the wrong operating system or browser manufacturer causes some
      sites in these languages to be garbled; Surfers to Eastern European
      sites should change it to something closer. And then some page access
      counters work by looking at the <span class="QUOTE">"Referer"</span>
      header; they may fail or break if unavailable. The weather maps of
      Intellicast have been blocked by their server when no <span class=
      "QUOTE">"Referer"</span> or cookie is provided, is another example.
      (But you can forge both headers without giving information away). There
      are many other ways things can go wrong when trying to fool a web
      server. The results of which could inadvertently cause pages to load
      incorrectly, partially, or even not at all. And there may be no obvious
      clues as to just what went wrong, or why. Nowhere will there be a
      message that says <span class="QUOTE">"<span class=
      "emphasis EMPHASIS c2">Turn off <tt class="LITERAL">fast-redirects</tt>
      or else!</span> "</span></p>

      <p>Similar thoughts apply to modifying JavaScript, and, to a lesser
      degree, HTML elements.</p>

      <p>If you have problems with a site, you will have to adjust your
      configuration accordingly. Cookies are probably the most likely
      adjustment that may be required, but by no means the only one.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="AEN891" id="AEN891">4.12. Can Privoxy act as
      a <span class="QUOTE">"caching"</span> proxy to speed up web
      browsing?</a></h3>

      <p>No, it does not have this ability at all. You want something like
      <a href="http://www.squid-cache.org/" target="_top">Squid</a> or
      <a href="http://www.pps.jussieu.fr/~jch/software/polipo/" target=
      "_top">Polipo</a> for this. And, yes, before you ask, <span class=
      "APPLICATION">Privoxy</span> can co-exist with other kinds of proxies
      like <span class="APPLICATION">Squid</span>. See the <a href=
      "../user-manual/config.html#FORWARDING" target="_top">forwarding
      chapter</a> in the <a href="../user-manual/index.html" target=
      "_top">user manual</a> for details.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="AEN901" id="AEN901">4.13. What about as a
      firewall? Can Privoxy protect me?</a></h3>

      <p>Not in the way you mean, or in the way some firewall vendors claim
      they can. <span class="APPLICATION">Privoxy</span> can help protect
      your privacy, but can't protect your system from intrusion attempts. It
      is, of course, perfectly possible to use <span class=
      "emphasis EMPHASIS c2">both</span>.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="AEN906" id="AEN906">4.14. I have large empty
      spaces / a checkerboard pattern now where ads used to be. Why?</a></h3>

      <p>It is technically possible to eliminate banners and ads in a way
      that frees their allocated page space. This could easily be done by
      blocking with <span class="APPLICATION">Privoxy's</span> filters, and
      eliminating the <span class="emphasis EMPHASIS c2">entire</span> image
      references from the HTML page source.</p>

      <p>But, this would consume considerably more CPU resources (IOW, slow
      things down), would likely destroy the layout of some web pages which
      rely on the banners utilizing a certain amount of page space, and might
      fail in other cases, where the screen space is reserved (e.g. by HTML
      tables for instance). Also, making ads and banners disappear without
      any trace complicates troubleshooting, and would sooner or later be
      problematic.</p>

      <p>The better alternative is to instead let them stay, and block the
      resulting requests for the banners themselves as is now the case. This
      leaves either empty space, or the familiar checkerboard pattern.</p>

      <p>So the developers won't support this in the default configuration,
      but you can of course define appropriate filters yourself to achieve
      this.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="AEN914" id="AEN914">4.15. How can Privoxy
      filter Secure (HTTPS) URLs?</a></h3>

      <p>Since secure HTTP connections are encrypted SSL sessions between
      your browser and the secure site, and are meant to be reliably
      <span class="emphasis EMPHASIS c2">secure</span>, there is little that
      <span class="APPLICATION">Privoxy</span> can do but hand the raw
      gibberish data though from one end to the other unprocessed.</p>

      <p>The only exception to this is blocking by host patterns, as the
      client needs to tell <span class="APPLICATION">Privoxy</span> the name
      of the remote server, so that <span class="APPLICATION">Privoxy</span>
      can establish the connection. If that name matches a host-only pattern,
      the connection will be blocked.</p>

      <p>As far as ad blocking is concerned, this is less of a restriction
      than it may seem, since ad sources are often identifiable by the host
      name, and often the banners to be placed in an encrypted page come
      unencrypted nonetheless for efficiency reasons, which exposes them to
      the full power of <span class="APPLICATION">Privoxy</span>'s ad
      blocking.</p>

      <p><span class="QUOTE">"Content cookies"</span> (those that are
      embedded in the actual HTML or JS page content, see <tt class=
      "LITERAL"><a href=
      "../user-manual/actions-file.html#FILTER-CONTENT-COOKIES" target=
      "_top">filter{content-cookies}</a></tt>), in an SSL transaction will be
      impossible to block under these conditions. Fortunately, this does not
      seem to be a very common scenario since most cookies come by
      traditional means.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="AEN928" id="AEN928">4.16. Privoxy runs as a
      <span class="QUOTE">"server"</span>. How secure is it? Do I need to
      take any special precautions?</a></h3>

      <p>On Unix-like systems, <span class="APPLICATION">Privoxy</span> can
      run as a non-privileged user, which is how we recommend it be run.
      Also, by default <span class="APPLICATION">Privoxy</span> listens to
      requests from <span class="QUOTE">"localhost"</span> only.</p>

      <p>The server aspect of <span class="APPLICATION">Privoxy</span> is not
      itself directly exposed to the Internet in this configuration. If you
      want to have <span class="APPLICATION">Privoxy</span> serve as a LAN
      proxy, this will have to be opened up to allow for LAN requests. In
      this case, we'd recommend you specify only the LAN gateway address,
      e.g. 192.168.1.1, in the main <span class="APPLICATION">Privoxy</span>
      configuration file and check all <a href=
      "../user-manual/config.html#ACCESS-CONTROL" target="_top">access
      control and security options</a>. All LAN hosts can then use this as
      their proxy address in the browser proxy configuration, but
      <span class="APPLICATION">Privoxy</span> will not listen on any
      external interfaces. ACLs can be defined in addition, and using a
      firewall is always good too. Better safe than sorry.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="TURNOFF" id="TURNOFF">4.17. Can I
      temporarily disable Privoxy?</a></h3>

      <p><span class="APPLICATION">Privoxy</span> doesn't have a transparent
      proxy mode, but you can toggle off blocking and content filtering.</p>

      <p>The easiest way to do that is to point your browser to the remote
      toggle URL: <a href="http://config.privoxy.org/toggle" target=
      "_top">http://config.privoxy.org/toggle</a>.</p>

      <p>See the <a href="../user-manual/appendix.html#BOOKMARKLETS" target=
      "_top">Bookmarklets section</a> of the <i class="CITETITLE">User
      Manual</i> for an easy way to access this feature. Note that this is a
      feature that may need to be enabled in the main <tt class=
      "FILENAME">config</tt> file.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="REALLYOFF" id="REALLYOFF">4.18. When
      <span class="QUOTE">"disabled"</span> is Privoxy totally out of the
      picture?</a></h3>

      <p>No, this just means all optional filtering and actions are disabled.
      <span class="APPLICATION">Privoxy</span> is still acting as a proxy,
      but just doing less of the things that <span class=
      "APPLICATION">Privoxy</span> would normally be expected to do. It is
      still a <span class="QUOTE">"middle-man"</span> in the interaction
      between your browser and web sites. See below to bypass the proxy.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="TURNOFF2" id="TURNOFF2">4.19. How can I tell
      Privoxy to totally ignore certain sites?</a></h3>

      <p>Bypassing a proxy, or proxying based on arbitrary criteria, is
      purely a browser configuration issue, not a <span class=
      "APPLICATION">Privoxy</span> issue. Modern browsers typically do have
      settings for not proxying certain sites. Check your browser's help
      files.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="CRUNCH" id="CRUNCH">4.20. My logs show
      Privoxy <span class="QUOTE">"crunches"</span> ads, but also its own
      internal CGI pages. What is a <span class=
      "QUOTE">"crunch"</span>?</a></h3>

      <p>A <span class="QUOTE">"crunch"</span> simply means <span class=
      "APPLICATION">Privoxy</span> intercepted <span class=
      "emphasis EMPHASIS c2">something</span>, nothing more. Often this is
      indeed ads or banners, but <span class="APPLICATION">Privoxy</span>
      uses the same mechanism for trapping requests for its own internal
      pages. For instance, a request for <span class=
      "APPLICATION">Privoxy's</span> configuration page at: <a href=
      "http://config.privoxy.org" target=
      "_top">http://config.privoxy.org</a>, is intercepted (i.e. it does not
      go out to the 'net), and the familiar CGI configuration is returned to
      the browser, and the log consequently will show a <span class=
      "QUOTE">"crunch"</span>.</p>

      <p>Since version 3.0.7, Privoxy will also log the crunch reason. If you
      are using an older version you might want to upgrade.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="DOWNLOADS" id="DOWNLOADS">4.21. Can Privoxy
      effect files that I download from a webserver? FTP server?</a></h3>

      <p>From the webserver's perspective, there is no difference between
      viewing a document (i.e. a page), and downloading a file. The same is
      true of <span class="APPLICATION">Privoxy</span>. If there is a match
      for a <tt class="LITERAL"><a href=
      "../user-manual/actions-file.html#BLOCK" target="_top">block</a></tt>
      pattern, it will still be blocked, and of course this is obvious.</p>

      <p>Filtering is potentially more of a concern since the results are not
      always so obvious, and the effects of filtering are there whether the
      file is simply viewed, or downloaded. And potentially whether the
      content is some obnoxious advertisement, or Mr. Jimmy's latest/greatest
      source code jewel. Of course, one of these presumably is <span class=
      "QUOTE">"bad"</span> content that we don't want, and the other is
      <span class="QUOTE">"good"</span> content that we do want. <span class=
      "APPLICATION">Privoxy</span> is blind to the differences, and can only
      distinguish <span class="QUOTE">"good from bad"</span> by the
      configuration parameters <span class="emphasis EMPHASIS c2">we</span>
      give it.</p>

      <p><span class="APPLICATION">Privoxy</span> knows the differences in
      files according to the <span class="QUOTE">"Content Type"</span> as
      reported by the webserver. If this is reported accurately (e.g.
      <span class="QUOTE">"application/zip"</span> for a zip archive), then
      <span class="APPLICATION">Privoxy</span> knows to ignore these where
      appropriate. <span class="APPLICATION">Privoxy</span> potentially can
      filter HTML as well as plain text documents, subject to configuration
      parameters of course. Also, documents that are of an unknown type
      (generally assumed to be <span class="QUOTE">"text/plain"</span>) can
      be filtered, as will those that might be incorrectly reported by the
      webserver. If such a file is a downloaded file that is intended to be
      saved to disk, then any content that might have been altered by
      filtering, will be saved too, for these (probably rare) cases.</p>

      <p>Note that versions later than 3.0.2 do NOT filter document types
      reported as <span class="QUOTE">"text/plain"</span>. Prior to this,
      <span class="APPLICATION">Privoxy</span> did filter this document
      type.</p>

      <p>In short, filtering is <span class="QUOTE">"ON"</span> if a) the
      content type as reported by the webserver is appropriate <span class=
      "emphasis EMPHASIS c2">and</span> b) the configuration allows it (or at
      least does not disallow it). That's it. There is no magic cookie
      anywhere to say this is <span class="QUOTE">"good"</span> and this is
      <span class="QUOTE">"bad"</span>. It's the configuration that lets it
      all happen or not.</p>

      <p>If you download text files, you probably do not want these to be
      filtered, particularly if the content is source code, or other critical
      content. Source code sometimes might be mistaken for Javascript (i.e.
      the kind that might open a pop-up window). It is recommended to turn
      off filtering for download sites (particularly if the content may be
      plain text files and you are using version 3.0.2 or earlier) in your
      <tt class="FILENAME">user.action</tt> file. And also, for any site or
      page where making <span class="emphasis EMPHASIS c2">any</span> changes
      at all to the content is to be avoided.</p>

      <p><span class="APPLICATION">Privoxy</span> does not do FTP at all,
      only HTTP and HTTPS (SSL) protocols.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="DOWNLOADS2" id="DOWNLOADS2">4.22. I just
      downloaded a Perl script, and Privoxy altered it! Yikes, what is
      wrong!</a></h3>

      <p>Please read above.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="HOSTSFILE" id="HOSTSFILE">4.23. Should I
      continue to use a <span class="QUOTE">"HOSTS"</span> file for
      ad-blocking?</a></h3>

      <p>One time-tested technique to defeat common ads is to trick the local
      DNS system by giving a phony IP address for the ad generator in the
      local <tt class="FILENAME">HOSTS</tt> file, typically using <tt class=
      "LITERAL">127.0.0.1</tt>, aka <tt class="LITERAL">localhost</tt>. This
      effectively blocks the ad.</p>

      <p>There is no reason to use this technique in conjunction with
      <span class="APPLICATION">Privoxy</span>. <span class=
      "APPLICATION">Privoxy</span> does essentially the same thing, much more
      elegantly and with much more flexibility. A large <tt class=
      "FILENAME">HOSTS</tt> file, in fact, not only duplicates effort, but
      may get in the way and seriously slow down your system. It is
      recommended to remove such entries from your <tt class=
      "FILENAME">HOSTS</tt> file. If you think your hosts list is neglected
      by <span class="APPLICATION">Privoxy's</span> configuration, consider
      adding your list to your <tt class="FILENAME">user.action</tt>
      file:</p>

      <table class="c3" border="0" width="100%">
        <tr>
          <td>
            <pre class="SCREEN">
  { +block }
   www.ad.example1.com
   ad.example2.com
   ads.galore.example.com
   etc.example.com
</pre>
          </td>
        </tr>
      </table>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="SEEALSO" id="SEEALSO">4.24. Where can I find
      more information about Privoxy and related issues?</a></h3>

      <p>Other references and sites of interest to <span class=
      "APPLICATION">Privoxy</span> users:</p>

      <table border="0">
        <tbody>
          <tr>
            <td><a href="http://www.privoxy.org/" target=
            "_top">http://www.privoxy.org/</a>, the <span class=
            "APPLICATION">Privoxy</span> Home page.</td>
          </tr>
        </tbody>
      </table>

      <table border="0">
        <tbody>
          <tr>
            <td><a href="http://www.privoxy.org/faq/" target=
            "_top">http://www.privoxy.org/faq/</a>, the <span class=
            "APPLICATION">Privoxy</span> FAQ.</td>
          </tr>
        </tbody>
      </table>

      <table border="0">
        <tbody>
          <tr>
            <td><a href="http://www.privoxy.org/developer-manual/" target=
            "_top">http://www.privoxy.org/developer-manual/</a>, the
            <span class="APPLICATION">Privoxy</span> developer manual.</td>
          </tr>
        </tbody>
      </table>

      <table border="0">
        <tbody>
          <tr>
            <td><a href="https://sourceforge.net/projects/ijbswa/" target=
            "_top">https://sourceforge.net/projects/ijbswa/</a>, the Project
            Page for <span class="APPLICATION">Privoxy</span> on <a href=
            "http://sourceforge.net" target="_top">SourceForge</a>.</td>
          </tr>
        </tbody>
      </table>

      <table border="0">
        <tbody>
          <tr>
            <td><a href="http://config.privoxy.org/" target=
            "_top">http://config.privoxy.org/</a>, the web-based user
            interface. <span class="APPLICATION">Privoxy</span> must be
            running for this to work. Shortcut: <a href="http://p.p/" target=
            "_top">http://p.p/</a></td>
          </tr>
        </tbody>
      </table>

      <table border="0">
        <tbody>
          <tr>
            <td><a href=
            "https://sourceforge.net/tracker/?group_id=11118&amp;atid=460288"
            target=
            "_top">https://sourceforge.net/tracker/?group_id=11118&amp;atid=460288</a>,
            to submit <span class="QUOTE">"misses"</span> and other
            configuration related suggestions to the developers.</td>
          </tr>
        </tbody>
      </table>

      <table border="0">
        <tbody>
          <tr>
            <td><a href="http://www.junkbusters.com/ht/en/cookies.html"
            target="_top">http://www.junkbusters.com/ht/en/cookies.html</a>,
            an explanation how cookies are used to track web users.</td>
          </tr>
        </tbody>
      </table>

      <table border="0">
        <tbody>
          <tr>
            <td><a href="http://www.junkbusters.com/ijb.html" target=
            "_top">http://www.junkbusters.com/ijb.html</a>, the original
            Internet Junkbuster.</td>
          </tr>
        </tbody>
      </table>

      <table border="0">
        <tbody>
          <tr>
            <td><a href="http://www.squid-cache.org/" target=
            "_top">http://www.squid-cache.org/</a>, a popular caching proxy,
            which is often used together with <span class=
            "APPLICATION">Privoxy</span>.</td>
          </tr>
        </tbody>
      </table>

      <table border="0">
        <tbody>
          <tr>
            <td><a href="http://www.pps.jussieu.fr/~jch/software/polipo/"
            target=
            "_top">http://www.pps.jussieu.fr/~jch/software/polipo/</a>,
            <span class="APPLICATION">Polipo</span> is a caching proxy with
            advanced features like pipelining, multiplexing and caching of
            partial instances. In many setups it can be used as <span class=
            "APPLICATION">Squid</span> replacement.</td>
          </tr>
        </tbody>
      </table>

      <table border="0">
        <tbody>
          <tr>
            <td><a href="https://www.torproject.org/" target=
            "_top">https://www.torproject.org/</a>, <span class=
            "APPLICATION">Tor</span> can help anonymize web browsing, web
            publishing, instant messaging, IRC, SSH, and other
            applications.</td>
          </tr>
        </tbody>
      </table>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="MICROSUCK" id="MICROSUCK">4.25. I've noticed
      that Privoxy changes <span class="QUOTE">"Microsoft"</span> to
      <span class="QUOTE">"MicroSuck"</span>! Why are you manipulating my
      browsing?</a></h3>

      <p>We're not. The text substitutions that you are seeing are disabled
      in the default configuration as shipped. You have either manually
      activated the <span class="QUOTE">"<tt class="LITERAL">fun</tt>"</span>
      filter which is clearly labeled <span class="QUOTE">"Text replacements
      for subversive browsing fun!"</span> or you are using an older Privoxy
      version and have implicitly activated it by choosing the <span class=
      "QUOTE">"Advanced"</span> profile in the web-based editor. Please
      upgrade.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="VALID" id="VALID">4.26. Does Privoxy produce
      <span class="QUOTE">"valid"</span> HTML (or XHTML)?</a></h3>

      <p>Privoxy generates HTML in both its own <span class=
      "QUOTE">"templates"</span>, and possibly whenever there are text
      substitutions via a <span class="APPLICATION">Privoxy</span> filter.
      While this should always conform to the HTML 4.01 specifications, it
      has not been validated against this or any other standard.</p>
    </div>

    <div class="SECT2">
      <h3 class="SECT2"><a name="SURPRISE-PRIVOXY" id=
      "SURPRISE-PRIVOXY">4.27. How did you manage to get Privoxy on my
      computer without my consent?</a></h3>

      <p>We didn't. We make Privoxy available for download, but we don't go
      around installing it on other people's systems behind their back. If
      you discover Privoxy running on your system and are sure you didn't
      install it yourself, somebody else did. You may not even be running the
      real Privoxy, but maybe something else that only pretends to be
      Privoxy, or maybe something that is based on the real Privoxy, but has
      been modified.</p>

      <p>Lately there have been reports of problems with some kind of Privoxy
      versions that come preinstalled on some Netbooks. Some of the problems
      described are inconsistent with the behaviour of official Privoxy
      versions, which suggests that the preinstalled software may contain
      vendor modifications that we don't know about and thus can't debug.</p>

      <p>Privoxy's <a href="copyright.html">license</a> allows vendor
      modifications, but the vendor has to comply with the license, which
      involves informing the user about the changes and to make the changes
      available under the same license as Privoxy itself.</p>

      <p>If you are having trouble with a modified Privoxy version, please
      try to talk to whoever made the modifications before reporting the
      problem to us. Please also try to convince whoever made the
      modifications to talk to us. If you think somebody gave you a modified
      Privoxy version without complying to the license, please let us
      know.</p>
    </div>
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